Nervous, Muscle, & Cardiovascular Systems
Supplemental Instruction
Iowa State University / Leader: / Sierra
Course: / AnS 214
Instructor: / Dr. Selsby
Date: / 3/5/2015
NERVOUS SYSTEM:
1) Explain how EPSPs and IPSPs work to influence events at the post-synaptic neuron. Also, give examples of synaptic relationships and whether they are generally EPSP’s or IPSP’s.
EPSP
· Neurotransmitters bind to open ligand gated Na+ and K+ channels
· Depolarizes the membrane – graded potential moves through cell
· Triggers action potential at axon hillock
· Opens voltage-gated channel
· Axodendritic
IPSP
· Neurotransmitters bind to open ligand gated Na+ and K+ channels
· Hyperpolarizes the membrane – more K+ moving out than Na+ moving in
· Reduces the potential for an action potential – must have a greater positive potential to overcome hyperpolarization
· Axosomatic
· Axoaxonic
2) Graph and describe an action potential. Be sure to include refractory periods, Na release, and K release in your answer.
*Be sure to know refractory periods as well
3) Explain the role of myelination in signal conduction. Also, note a difference between the CNS and the PNS in your answer.
· Fat cells wrap plasma membranes around axon of neuron
· Speeds up conduction by not allowing Na+ out or K+ in at high levels under myelinated areas
· Low concentration of ion channels under myelination keeps ion concentrations fairly constant
· CNS – oligodendrocytes, one wraps around many nerves
· PNS – schwann cells, one schwann cell per nerve
4) Describe how an action potential is propagated from the pre-synaptic neuron to the post-synaptic neuron.
· Starts at the presynaptic axon terminal
· Synaptotagmin protein binds Ca+2 and promotes fusion of synaptic vesicles with the axon membrane
· Exocytosis of neurotransmitter
· Neurotransmitter binds to receptors on postsynaptic neuron
· Causes IPSP or EPSP
MUSCLE SYSTEM:
1) Explain the events that take place at the neuromuscular junction generating an action potential. Explain how that potential is propagated along the muscle cell in relation to the triad (t-tubule and two terminal cisternae).
· ACh released from neuron binds to receptors on muscle to cause an EPSP
· Opens ligand gated channels that release Na+ and K+
· Generates an action potential if threshold is reached
· Action potential moves on the outside of the muscle cell into the t-tubule (still outside the cell)
· Positively charged action potential attracts electron dense feet away from the opening to the sarcoplasmic reticulum/terminal cisternae
· Ca+2 released into the cell and the cross bridge cycle can take place
2) Explain what is meant by excitation-contraction coupling. Compare and contrast the steps involved in EC coupling in skeletal muscle and cardiac muscle.
· Action potential leads to sliding of myofilaments and contraction of the sarcomere
· Action potential propagates to t-tubules along muscle cells
· Electron dense feet move allowing the release of Ca+2 into the muscle cell
· Ca+2 binds to TNc
· Troponin changes shape to physically move tropomyosin away from the active sites
· Myosin can bind to actin on the uncovered active sites and the muscle contracts
· May be a Ca+2 surge in muscle, but definitely in cardiac cells
3) Explain what events must occur on the myofibril level in order for a muscle contraction and relaxation to take place. In your answer draw the four stages of the cross-bridge cycle. Indicate which stage is high or low energy.
4) What happens to motor units with age and what are the implications of this?
· Motor neurons begin to die from non-use
· This leaves muscle fibers in the muscle without any innervation
· They are then recruited by other motor neurons effectively increasing the size of the smallest motor units in the muscle
· Lose the mosaic pattern of muscle and fine motor skills as the motor units get larger
CARDIOVASCULAR SYSTEM:
1) Trace the electrical events involved in cardiac contraction. Be able to explain what would happen if one part was extracted.
· SA node depolarizes – pacemaker of a normal heart
· Conducts signal to AV which connects the atrium to the ventricle
· Signal is then conducted to the AV bundle/bundle of His
· Continues into the bundle branches in the septum of the heart, carries the signal to the apex of the heart
· Purkinje fibers in the apex and outer walls of the ventricles carry the signal from the bottom up
· Remove SA node – AV node takes over, ectopic focus, heart rate around 40-60 bpm
· Remove AV node – ventricles will not contract, not compatible with life
2) Explain electrocardiography by drawing a normal EKG and explaining its elements, and then giving examples of cardiac abnormalities that can be detected using this diagnostic tool.
· P wave – atrial depolarization
· QRS complex – ventrical depolarization, atrial repolarization
· T wave – ventrical repolarization
· Fibrillation
· Arrhythmia
· Premature ventricular contraction
· Defective SA node
3) Describe the relationship between exercise and cardiac output. What other factors can affect CO?
· Exercise increases heart rate due to sympathetic activity
· This increases the venous return of blood to the heart and an increase in stroke volume as the heart fills with more blood
· Increase in stroke volume and heart rate increase cardiac output
· Can cause hypertrophy of cardiac cells – larger stroke volume with a stronger muscle contraction, lower heart rate for same cardiac output
· Age, gender, body temperature
4) Compare the action potentials between the Nervous, Muscular, and Cardiovascular Systems.
Nervous
· Na+ and K+ movement
· EPSP or IPSP
· Many neurotransmitters
Muscles
· Na+ and K+ movement
· ACh for muscle contractions
· Ca+2 thought to be part of de/repolarization process
Cardiac
· Na+ and K+ movement
· Ca+2 definitely moves during action potential propagation
· Slower repolarization due to Ca+2
· Long absolute refractory period due to Ca+2